Phosphorus only based flame retardants (“FRs”) are typically not effective on nylon. It has been noted that in many cases phosphorus treated nylon fabrics will burn at a greater rate than the untreated fabric. It is believed that in the combustion process the phosphorus containing material forms an acidic environment which causes the nylon polymer to unzip to supply more fuel for combustion. In theory the combustion matrix needs a component that will lower the “acidity” during combustion to minimize the “unzipping” of the nylon polymer.
Many of the phosphorus containing systems for nylon require a halogen with the phosphorus system to be effective. It is not sure how the bromine works but it is assumed that it serves as a free radical scavenger as well as possibly modifying the melt properties of the nylon polymer. However, there is a trend in the industry to minimize the use of halogens as FR materials due to environmental concerns.
The use of sulfur containing materials has been used for years to treat nylon composites to meet various FR standards. The more common systems are based on thiourea and formaldehyde components. However, the hand of the treated fabrics is usually very stiff and there is an odor associated with the finished product. The finished product also has a high level of formaldehyde present. The mechanism of the sulfur containing materials for reducing the flammability is based on modifying the melt behavior of the nylon polymer.
For nylon/cotton blends with 10 percent or higher of nylon, there is generally a molten puddle of the nylon polymer present with flame front in the combustion process, even with FR treated fabrics. In a fire it is perceived that this molten puddle of nylon sticks to the skin of a person wearing the garment and can seriously burn the person. FR cellulosic containing fabrics form a char which helps to provide some insulation to minimize the burn injuries. On the other hand, 100% synthetic containing fabrics and high nylon containing blends can melt and stick to the skin causing serious burns more so than cellulosic fabrics.
Fabric and clothing manufacturers continue to seek improvements in FR fabrics and methods for manufacturing FR fabrics.